Wireless charger having E-field shield

ABSTRACT

A shielding arrangement for preventing AM radio interference when a wireless charger is used in a vehicle has a plurality of parallel conductors arranged at a distance from one another responsive to a frequency desired to be attenuated. An interconnection arrangement includes a solid conductive junction and connects the conductors to one another without forming loops, and to ground. The conductors are traces disposed on a PCB. Additional parallel conducts are disposed on the other side of the PCB at an orthogonal orientation with respect to the first conductors. The spacing between the conductors is determined in response to the frequency desired to be attenuated, as well as frequencies thereabove that are desired to be propagated therethrough, such as mobile telephone signals. The solid conductive junction that is disposed on the printed circuit board is electrically and thermally conductive, such as copper.

This application is a divisional application of co-pending U.S.application Ser. No. 13/613,282, filed Sep. 13, 2012, of which thisapplication is incorporated by reference herein in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to electrical power systems thatproduce undesired electromagnetic fields and heat, and moreparticularly, to a shielding arrangement that is particularly useful incharging systems for chargeable devices, wherein the propagation ofelectromagnetic fields and heat is attenuated, but magnetic fields arepermitted to pass with minimal eddy current losses. This inventionrelates generally to electrical power systems that produce undesiredelectromagnetic fields and heat, and more particularly, to a shieldingarrangement that is particularly useful in charging systems forchargeable devices, wherein the propagation of electromagnetic fieldsand heat is attenuated, but magnetic fields are permitted to pass withminimal eddy current losses.

2. Description of the Related Art

Wireless charging systems transfer energy between a primary andsecondary coil by creating a time variant magnetic field in the primarycoil. This magnetic field also creates a similar time variant electricfield or E-field. The fundamental frequency of this primary signal canbe designed to lie below the AM radio band in an attempt to avoidinterfering with the AM radio reception in a vehicle application.

However, it is expensive, and inefficient from the standpoint of powerutilization, to eliminate the harmonics of the primary signal that spillover into the AM band and interfere with AM radio reception. There istherefore a need in the art to reduce AM band interference cause bywireless charging systems.

The prior art has sought to address issues related to magneticinterference by providing magnetic shielding around the outer volume ofthe primary secondary system. However, the prior art does not seem toaddress the particular concerns of an automotive application of wirelesscharging and its interference with the AM radio reception.

Another problem inherent in wireless charging is the temperature rise ofthe charger surface that contacts the chargeable device. Excessivetemperature rise of this surface will cause the chargeable device toterminate charging in order to protect itself from overheating. Thedifficulty in removing the waste heat from the charging coil is thatthere can be no conductive loop established above the coil because ofeddy current formation. Therefore, a solid electrically conductivematerial cannot be placed above the coil to function as a heat sink.

There is therefore in the art a need for a wireless charging arrangementthat, in addition to reducing, and preferably eliminating, AM bandinterference, the wireless charging arrangement does not cause thecharger surface to generate excessive heat.

It is, therefore, an object of this invention to provide a wirelesscharging arrangement for a handheld device that does not cause undueheat to be transferred to the handheld device.

It is another object of this invention to provide a system forattenuating electromagnetic energy stemming from an electrical apparatusthat would cause interference in a frequency range of interest totransmission of information.

It is also an object of this invention to provide a system forattenuating electromagnetic energy that would interfere with radiotransmission signals.

It is a further object of this invention to provide a system forattenuating electromagnetic energy that would interfere with radiotransmission signals of a predetermined frequency range, but wouldpermit radio signals of a different frequency range to pass throughsubstantially without being attenuated.

SUMMARY OF THE INVENTION

The foregoing and other objects are achieved by this invention whichprovides, in accordance with a first apparatus aspect thereof, ashielding arrangement having a plurality of substantially parallelconductors arranged at a first predetermined lateral distance from oneanother. The first predetermined lateral distance is responsive to afrequency of an electromagnetic energy that is desired to be attenuatedas the electromagnetic energy is propagated through the shieldingarrangement. There is additionally provided an interconnectionarrangement for connecting the plurality of substantially parallelconductors to one another.

In one embodiment of this first apparatus aspect of the invention, thereis further provided a printed circuit board, and the plurality ofsubstantially parallel conductors constitute conductive traces that aredisposed on a first side of the printed circuit board.

In a further embodiment, the interconnection arrangement includes asolid conductive junction disposed on the printed circuit board.

In a still further embodiment of the invention, the printed circuitboard has a second side, and there is provided a further plurality ofsubstantially parallel conductors arranged at a second predeterminedlateral distance from one another. The further plurality ofsubstantially parallel conductors have a predetermined angularorientation with respect to the plurality of substantially parallelconductors. In some embodiments, the predetermined angular orientationis a substantially orthogonal angular orientation.

The first and second predetermined lateral distances are equal to eachother in some embodiments of the invention. Also, there is provided insome embodiments a further interconnection arrangement for connectingthe further plurality of substantially parallel conductors to oneanother. In an advantageous embodiment, the further interconnectionarrangement is the previously described solid conductive junction thatis disposed on the printed circuit board.

In a further advantageous embodiment of the invention, the solidconductive junction disposed on the printed circuit board is configuredto conduct heat. Therefore, it is advantageous that the solid conductivejunction that is disposed on the printed circuit board be formed of amaterial that is electrically and thermally conductive. An excellentmaterial for this purpose is a metallic material that contains copper.

In accordance with a further apparatus aspect of the invention, there isprovided a wireless charging arrangement for a handheld device. Inaccordance with this further aspect of the invention, the wirelesscharging arrangement is provided with a primary charging coil that hasan electrical input for receiving input electrical pulses. The inputelectrical pulses urge the primary charging coil to issue a time-varyingmagnetic field and a time-varying electric field. Both such fields areresponsive to the input electrical pulses. There is additionallyprovided an E-field shield that attenuates the time-varying electricfield.

In one embodiment of this further apparatus aspect of the invention, thetime-varying electric field contains a frequency component that wouldcause interference in the AM radio transmission band. Thus, the E-fieldshield is configured to attenuate the interfering frequency component ofthe time-varying electric field.

In an advantageous embodiment of this further apparatus aspect, theE-field shield is configured to prevent the creation of eddy currents inthe time-varying magnetic field.

In a further advantageous embodiment of this aspect of the invention,the E-field shield is configured to permit propagation therethrough ofelectromagnetic signals having frequencies above those of the AM radiotransmission band. This characteristic of the E-field shield isparticularly useful in embodiments of the invention where the E-fieldshield is arranged to surround around the wireless charging arrangement.In other embodiments, however, the E-field shield is interposed betweenthe primary charging coil and the handheld device.

In accordance with a method aspect of the invention, there is provided amethod of reducing AM radio interference when using a wireless chargingarrangement to charge an internal battery of handheld device. The methodincludes the step of interposing an E-field shield between the wirelesscharging arrangement and an affected AM radio receiver.

In one embodiment of this method aspect, the step of interposing anE-field shield between the wireless charging arrangement and an affectedAM radio receiver includes the step of interposing a first plurality ofsubstantially parallel conductors arranged at a first predeterminedlateral distance from one another, the first predetermined lateraldistance being responsive to a frequency of an electromagnetic energythat is desired to be attenuated as the electromagnetic energy ispropagated through the shielding arrangement.

In a further embodiment, the step of interposing an E-field shieldbetween the wireless charging arrangement and an affected AM radioreceiver includes the step of interposing between the wireless chargingarrangement and an affected AM radio receiver a further plurality ofsubstantially parallel conductors arranged at the first predeterminedlateral distance from one another, the further plurality ofsubstantially parallel conductors having a predetermined angularorientation with respect to the first plurality of substantiallyparallel conductors.

As noted, the proposed solution to the AM interference problem inaccordance with one embodiment of the present invention is the additionof an E-field shield disposed above the primary coil such that itattenuates the AM band field but allows the magnetic field to passthrough with no significant eddy current losses in the shield layer.Eddy currents reduce efficiency in a wireless charger embodiment.Preferably, the shield is made of thermally conductive material therebyaffording the added benefit of dissipating heat away from the coil area.In areas surrounding, but not directly over, the coil, this shield insome embodiments of the invention is solid, thereby improving its heatsinking ability.

In other embodiments, an E-field shield is arranged around a portion ofthe charger system including the primary and the secondary elements.This may take the form in some embodiments of a complete six-sidedenclosure, or it may simply be a single plane of shielding interposedbetween the charging system and the AM antenna of an affected AM radioreceiver.

The solution proposed in accordance with the present invention is costeffective since the shield can be integrated into the printed wiringboard (PWB) based primary coil top layer, or it could be added as asecondary PWB placed on top of the primary coil. A similar shieldingconcept can in some embodiments be applied to wire wound primary coils,but the overall cost and structural advantage is not as pronouncedcompared to the PWB based primary coil implementation.

Some of the key characteristics of the inventive E-field shield are:

1) The thickness of the shield should be as small as possible so that itdoes not significantly increase the nominal gap between the primary andsecondary coil. A larger nominal gap reduces the useful range of the airgap in the application of a wireless charger;

2) There must be no closed loops in the conductive pattern of theE-field shield because closed loops support eddy currents that producecharging inefficiency and create unwanted temperature rise in thecharger housing;

3) The width of the conductors in the E-field shield pattern should benarrow enough to reduce eddy currents in the individual traces;

4) The spacing of the E-field shield traces should be close enough toshield AM signals but in the case of the full system shield should befar enough apart to allow mobile phone signals to pass;

5) The shield traces should be electrically conductive, but magneticallyneutral; and

6) The shield traces should be connected to the negative voltagereference of the vehicle.

In some embodiments of the invention, the E-field shield assists in thedissipation of the charger coil waste heat by providing a solid copperpattern in areas of the shield that are not directly above the coil. Theeffectiveness of the E-field shield pattern is enhanced if the E-fieldshield is made of a material that is highly electrically conductive.Moreover, significant advantages are achieved if the material is highlythermally conductive for enhancing the heat sink function. Copper is anexcellent material for both parameters, as it is an excellent electricaland thermal conductor. The same vias that are used to ground the shieldconductor can also serve as thermal vias to the grounded aluminum heatsink in the charger that is also at ground potential.

In a specific illustrative embodiment of the invention, the distancebetween the adjacent conductors of the shielding mat is spaced less thanthe ¼ wavelength of the frequencies that are desired to be attenuated.Thus, the spacing of the E-field shield traces are close enough toshield AM signals, and in embodiments of the invention that employ afull system shield, the conductive traces are far enough apart to permitthe passage there through of mobile phone signals. In such embodiments,it is desired to attenuate the radiation in the AM band, illustratively˜150 kHz to ˜1.71 MHz. Measurements using a rod antenna illustrate theeffectiveness of the attenuation achieved with the present inventiveshield system.

BRIEF DESCRIPTION OF THE DRAWINGS

Comprehension of the invention is facilitated by reading the followingdetailed description, in conjunction with the annexed drawing, in which:

FIG. 1 is a plan representation of one side of an E-field shieldconstructed in accordance with the principles of the invention depictingplural electrically conductive traces arranged longitudinally;

FIG. 2 is a plan representation of the other side of the E-field shieldof FIG. 1 depicting plural electrically conductive traces arrangedsubstantially orthogonally relative to the electrically conductivetraces on the side shown in FIG. 1;

FIG. 3 is a simplified schematic representation of a wireless chargerarrangement in which an E-field shield constructed in accordance withthe principles of invention is interposed between the charger base andthe receiver;

FIG. 4 is a simplified schematic representation of a wireless chargerarrangement in which an E-field shield constructed in accordance withthe principles of invention is arranged to surround the charger base andthe receiver;

FIG. 5 is a highly simplified block and line representation of aspecific illustrative embodiment of the invention shown in the contextof a wireless charger arrangement, the E-field shield of the presentinvention being applied to limit AM band interference from a planarcharger coil;

FIG. 6 is a simplified schematic representation of a circuit board thatis useful in a single mat module of a wireless charger arrangement thatemploys the E-field shield of the present invention;

FIG. 7 is a simplified schematic representation of a heat sink andprimary coil arrangement that is useful in a single mat module of awireless charger arrangement that employs the E-field shield of thepresent invention;

FIG. 8 is a partially exploded representation that illustrates anarrangement of a printed circuit board, a Nomex® layer, a heat sinklayer, a coil layer, and two magnets for forming a wireless chargerarrangement;

FIG. 9 is a simplified cross-sectional representation of the arrangementof FIG. 8;

FIG. 10 is a simplified schematic isometric representation of an E-fieldshield constructed in accordance with the invention overlying a printedcircuit board; and

FIGS. 11(a) and 11(b) are graphical representations that illustrate themagnitude as a function of frequency distribution of AM interferencefrom a wireless charging arrangement without E-field shielding, and theattenuation that is achieved with the E-field shielding of the presentinvention.

DETAILED DESCRIPTION

FIG. 1 is a plan representation of one side of an E-field shield 100constructed in accordance with the principles of the invention, anddepicts plural electrically conductive traces 102 arrangedlongitudinally on a circuit board 104. In this specific illustrativeembodiment of the invention, circuit board 104 is configured for usewith a wireless charger (not shown) for a handheld device (not shown).Electrically conductive traces 102 are electrically coupled to oneanother at solid patterns 110, and do not form, in this embodiment, anyclosed loops. The solid patterns, in this embodiment, are formed ofcopper and are arranged so as not to be located in the region (notspecifically designated) of circuit board 104 that would be near thecharging coil (not shown in this figure) of the wireless charger.

Electrically conductive traces 102 are separated from one another by adistance that is, in some embodiments, responsive to the frequency ofthe electrical energy that is desired to be attenuated. In the presentembodiment, it is desired to attenuate electromagnetic energy that wouldinterfere with the AM radio band, as would be the case with a wirelesscharger arrangement intended for use in a vehicle. As noted above, it isin this illustrative embodiment of the invention desired to attenuatethe propagation of electromagnetic radiation in the AM band,illustratively ˜150 kHz to ˜1.71 MHz. The inter-trace spacing thereforemust be smaller than the quarter wavelength of the highest frequencydesired to be attenuated. However, in embodiments of the invention wherethe handheld device (not shown) that is desired to be charged is amobile telephone, the inter-trace spacing must be large enough to permitmobile telephone signals to pass through the E-field shield, inembodiments where the mobile telephone it disposed within the shieldedregion, as will be discussed below.

FIG. 2 is a plan representation of the other side of E-field shield 100,shown in FIG. 1, depicting plural electrically conductive traces 112arranged substantially orthogonally relative to the electricallyconductive traces on the side shown in FIG. 1, on circuit board 104.Elements of structure that have previously been discussed are similarlydesignated. In FIGS. 1 and 2, solid patterns 110 serve as groundingpoints, as it is desirable that the conductive traces be at groundpotential. Also in this embodiment, solid patterns 110 serve to conductheat away from the region where the handheld device to be charged isdisposed, as will be described hereinbelow.

FIG. 3 is a simplified schematic representation of a wireless chargerarrangement in which an E-field shield 36, constructed in accordancewith the principles of invention, is interposed between a charger base32 and a receiver 34.

FIG. 4 is a simplified schematic representation of a wireless chargerarrangement in which an E-field shield 46 constructed in accordance withthe principles of invention is arranged to surround a charger base 42and a receiver 44. In this embodiment, The handheld device (not shown)desired to be charged (not specifically designated) encloses receiver 44and is enclosed within the E-field shield, and therefore the inter-trace(or inter-conductor) spacing of the E-field shield must be large enoughto enable mobile telephone signals to pass there through. Persons ofskill in the art can configure the inter-trace spacing small enough toblock transmission of electromagnetic radiation that would interferewith the conventional AM band, yet be large enough to enable thesignificantly higher frequencies of mobile telephone communicationsignals to pass through. Thus, when used in a vehicle, AM radio bandinterference is attenuated, but the mobile telephone remains active andusable to receive telephone calls.

FIG. 5 is a highly simplified block and line representation of aspecific illustrative embodiment of the invention shown in the contextof a wireless charger arrangement 50. In this embodiment, E-field shield52 of the present invention (shown simplified and in phantom) is appliedto attenuate the propagation of AM band interference signals (not shown)that originate from a primary charging coil 54 (representedschematically). The E-field shield is shown in this figure to overliethe primary charging coil, which in some embodiments is formed byprinting corresponding conductive traces onto a printed wiring board(not shown in this figure).

As shown in this figure, a micro controller 56 receives operating powerfrom a power supply 57 that also supplies electrical energy to a pulsepower module 58. The micro controller manages delivery of system powerpulses (not shown) to the primary charging coil via the pulse powermodule. The electrical pulses issued by pulse power module 58 containfrequency components that are converted by primary charging coil 54 intoemissions (not shown) that contain radio frequency components thatinterfere with AM radio transmissions. Thus, when such a wirelesscharger is employed in a vehicle (not shown) whereby the wirelesscharger is in proximity of an AM radio (not shown), it is necessary tosuppress such interference signals. In this regard, it is noted thatprimary charging coil 54 issues a time-varying magnetic field and atime-varying electric field, neither of which is shown in the figure,that are responsive to the input electrical pulses. E-field shield 52,as described herein, attenuates the propagation of the interferencesignals while creating minimal if any eddy currents in, or attenuationof, the time varying magnetic field.

Although primary charging coil 54 and E-field shield 52 are shown inthis specific illustrative embodiment of the invention to havesubstantially planar configurations, it is to be understood that othercoil and shield configurations can be employed in the practice of theinvention. As will be discussed below, the E-field shield can in someembodiments have a flexible characteristic allowing such shielding to beapplied to attenuate determined frequency components of E-fieldemissions from non-planar coils. Also, as noted, the E-field shield canin other embodiments of the invention be configured to surround theentirety of the wireless charger unit, and in still further embodiments,surround the entire wireless charger unit and the handheld device beingcharged.

FIG. 6 is a simplified schematic representation of a circuit board 64that is useful in a single mat module (not shown) of a wireless chargerarrangement that employs the E-field shield (not shown in this figure)of the present invention. In this embodiment, circuit board 64 has athickness of approximately 1.00 mm, and overall plan dimensions ofapproximately 51.5 mm (vertically in the drawing) and a width ofapproximately 52.50 mm. A semi-circular notch region 66 has a radiusdimension of approximately 9.00 mm, and a rectangular notch 67 has adepth of approximately 6.5 mm and a dimension along the edge of circuitboard 64 of approximately 16 mm. The four apertures 61 have a diameterof approximately 4.4 mm.

FIG. 7 is a simplified schematic representation of a heat sinkarrangement 74 that is useful in a single mat module of a wirelesscharger arrangement that employs the E-field shield of the presentinvention. Heat sink arrangement 74 has disposed thereon a primary coil72. In this embodiment, primary coil 72 is configured as a printedcircuit board formed of commercially available ferrite and Nomex®.

FIG. 8 is a partially exploded representation that illustrates anarrangement of printed circuit board 64, a Nomex® layer 82, heat sinklayer 74, coil layer 72, and two permanent magnets 84 and 86 for forminga wireless charger arrangement (not specifically designated). Elementsof structure that have previously been discussed are similarlydesignated. As is seen from this figure, coil layer 72 and heat sink 74are maintained separated from printed circuit board 64 by Nomex® layer82.

FIG. 9 is a simplified cross-sectional representation of the arrangementof FIG. 8. Elements of structure that have previously been discussed aresimilarly designated. There is shown in this figure a stackedarrangement of printed circuit board 64, Nomex® layer 82, heat sinklayer 74, coil layer 72, and permanent magnets 84 and 86. Permanentmagnets 84 and 86 are useful to ensure that the handheld device (notshown) remains in position centered over primary coil 72.

FIG. 10 is a simplified schematic isometric representation of an E-fieldshield 1002 constructed in accordance with the invention overlying aprinted circuit board 1004. As shown in this figure, E-field shield 1002has a plurality of conductors 1003 that are spaced sufficiently close toattenuate electromagnetic energy that would cause interference with AMband radio signals. As previously described, the conductors are notlooped, so as to prevent the formation of eddy currents and are coupledelectrically to solid printed areas 1006. In some embodiments, such aswhere conductive traces are included on the unseen side of E-fieldshield 1002, those conductive traces are also connected to solid printedareas 1006.

It is seen from FIG. 10 that E-field shield 1002 is arranged to overliea printed board 1004, that contains circuitry that, if not shielded,would issue electromagnetic radiation that would cause interference inthe AM radio frequency band. In addition, E-field shield 1002 is shownto be somewhat flexible, and accordingly, the invention is not limitedto inflexible substrates. Although not seen in this figure, in someembodiments of the invention that is provided a primary coil directly onprinted circuit board 1004.

FIGS. 11(a) and 11(b) are graphical representations that illustrate themagnitude as a function of frequency distribution of AM interferencesignal issued from a wireless charging arrangement without E-fieldshielding, and the attenuation that is achieved with the E-fieldshielding of the present invention. As shown in FIG. 11(a), the signaltrace that has been received by a test rod antenna (not shown) in awireless charger arrangement that has not been shielded in accordancewith the invention has a magnitude of 67.699 dBμV/m at 1.034000 MHZ. Incontrast, FIG. 11(b) shows that with the use of the inventive shieldingsystem, the signal trace at 1.034000 MHZ is only 39.558 dBμV/m. Thepresent embodiment of the invention is therefore seen to be effective atattenuating the issued interference signal in the AM band.

Although the invention has been described in terms of specificembodiments and applications, persons skilled in the art can, in lightof this teaching, generate additional embodiments without exceeding thescope or departing from the spirit of the claimed invention.Accordingly, it is to be understood that the drawing and description inthis disclosure are proffered to facilitate comprehension of theinvention, and should not be construed to limit the scope thereof.

The invention claimed is:
 1. A wireless charging arrangement forcharging a handheld device, the wireless charging arrangementcomprising: a primary charging coil having an electrical input forreceiving input electrical pulses, the input electrical pulses causingthe primary charging coil to radiate a time-varying magnetic field and atime-varying electric field, responsive to the input electrical pulses;and an E-field shield that attenuates the time-varying electric field,the E-field shield interposed between the primary charging coil and thehandheld device, and including: a first plurality of substantiallyparallel conductors disposed on a first side of a printed circuit board;a second plurality of substantially parallel conductors disposed on asecond side of the printed circuit board in a substantially orthogonalangular orientation relative to the first parallel conductors, thesecond side of the printed circuit board being coplanar with andopposite the first side of the printed circuit board.
 2. The wirelesscharging arrangement of claim 1, wherein the time-varying electric fieldcontains frequency components in the AM radio transmission band, andsaid E-field shield is configured to attenuate a component of thetime-varying electric field that would create interference withelectromagnetic signals in the AM radio transmission band.
 3. Thewireless charging arrangement of claim 2, wherein said E-field shield isconfigured to prevent the creation of eddy currents in the time-varyingmagnetic field.
 4. The wireless charging arrangement of claim 2, whereinsaid E-field shield is configured to permit propagation therethrough ofelectromagnetic signals having frequencies above those of the AM radiotransmission band.
 5. The wireless charging arrangement of claim 4,wherein said E-field shield is arranged to surround around the wirelesscharging arrangement.
 6. The wireless charging arrangement of claim 3,wherein said E-field shield is interposed between said primary chargingcoil and the handheld device.